Prior art patent document published under EP 1 327 809 A1 discloses a high pressure gas valve with an electromagnetic actuator. The valve comprises a main gas shut-off device and an auxiliary one. The main gas shut-off device comprises a seat formed in the valve body and a movable closure member. The valve comprises an auxiliary chamber on the side of the movable closure member that is opposite to the seat. The movable closure member comprises a central gas passage connecting the auxiliary chamber with the outlet of the valve. The auxiliary chamber is permanently connected with the inlet through a passage of reduced cross area. The electromagnetic actuator comprises a first plunger that is slidably received in the auxiliary chamber, the chamber being surrounded by an electric coil. The first plunger and the movable closure member form the auxiliary gas shut-off device. A second plunger is also slidably received in the chamber. A pin extends through the first plunger so as to abut, at one end, against the second plunger and, at the other end, against the movable closure member. When the electric coil is energized, a magnetic field is created in the first and second plungers and these are attracted to each other. The pin is then pushed by the second plunger so as to keep the movable closure member at a distance from the first plunger. The auxiliary gas shut-off device then opens and the high pressure gas present in the auxiliary chamber flows to the outlet through the central gas passage. The pressure in the auxiliary chamber drops as a result of the reduced cross area of the passage connecting the chamber with the inlet. The drop of pressure in the auxiliary chamber causes the closure member to move in an opening direction. Indeed, the opening force resulting from the high pressure of the inlet acting on an annular surface of the closure member was compensated by a closing effort of a higher magnitude, this effort resulting from the same pressure acting on a larger central surface on the opposite face of the closure member. When the pressure in the auxiliary pressure drops, this compensation is not more active and the closure member moves in an opening direction. When the coil is not more energized, the attracting force between the first and second plungers disappears and the spring between the plungers moves the first plunger towards the movable closure element and closes the auxiliary shut-off device. The pressure in the auxiliary chamber builds then up again and causes the closure element to move towards its seat for closing the valve.
This kind of valve construction is interesting for high pressure gas, i.e., largely above 200 bar. The effort that is necessary to exert on the plunger for closing the valve is reduced in view of the reduced cross section of the auxiliary seat. Additionally, this type of valve is normally closed.
This valve construction causes however embrittlement problems when used with hydrogen. Indeed, hydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen. The mechanism starts with lone hydrogen atoms diffusing through the metal. At high temperatures and/or high pressure, the elevated solubility of hydrogen allows hydrogen to diffuse into the metal. When these hydrogen atoms re-combine in minuscule voids of the metal matrix to form hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase to levels where the metal has reduced ductility and tensile strength up to the point where it cracks open (hydrogen induced cracking, or HIC). High-strength and low-alloy steels, nickel and titanium alloys are most susceptible to embrittlement.
In the above mentioned patent document EP 1 327 809 A1, the magnetic elements like the annular core extending through the coil and forming the chamber in which the first and second plunger are slidably received must in principle be made of magnetic material, i.e., ideally ferrous material but also high-strength steel. When using this valve with hydrogen, in particular at very high pressure like above 200 bar or even 500 bar, embrittlement can occur in all body parts of the valve that are in contact with hydrogen.